1. Field of the Invention
The present invention relates to an adaptive equalizer for waveform equalization of a replay signal of data recorded on a recording medium or the like, and in particular, to control of filter coefficients of a variable filter used for equalization.
2. Description of the Related Art
In a magnetic replay device for replaying magnetic data recorded on a magnetic recording medium, an adaptive equalizer is used for compensating amplitude distortion or phase distortion of the replay signal from a magnetic head (refer to, for example, Japanese Patent Laid-Open Publication No. Hie 5-40907).
In the adaptive equalizer, an equalization process is applied to an input signal by an FIR (Finite Impulse Response) filter. An output of the FIR filter is supplied to a decoding circuit and a data sequence is decoded through determination of “1” and “0” by level comparison or the like. A difference between an output from the decoding circuit and an output from the FIR filter is calculated and sent to an adaptive controller unit. The adaptive controller unit adaptively updates filter coefficients of the FIR filter so that a signal power of the difference is minimized.
In an adaptive equalization of determination feedback as described above, when a state continues in which an input signal is significantly different from the equalization target characteristic such as, for example, when there is damage to the magnetic tape, the filter coefficients diverge and cannot converge to the target equalization characteristic. As a result, video data and audio data cannot be properly reconstructed.